The present invention relates to the transmission of data in a layered data communication scheme, and is particularly applicable to the transmission of upstream messages in a hybrid fiber coaxial network. The invention is useful, for example, in allowing subscriber units to communicate messages to a central controller (e.g., cable television headend) for Internet access, videoconferencing, audio communication or the like. Bandwidth is dynamically allocated to subscribers of the network by the central controller according to the overall available bandwidth, the amount of bandwidth which is currently being used by each subscriber, and the number of current subscribers, among other factors.
In the past, cable television systems have utilized coaxial cable to carry signals from a headend to individual subscriber units. With the advent of new digital television services as well as the desire to carry data to and from subscriber units, the increased bandwidth provided by fiber optic cable has become attractive. Implementation of optical fiber networks all the way from the headend to individual subscriber units is not currently a practical alternative due to the high cost of building an optical fiber plant in which fiber is run all the way to individual homes. As a compromise, hybrid fiber coax (HFC) plants are being implemented. In HFC systems, fiber is run from the headend to neighborhood hubs. Existing coaxial cable is then coupled to receive the signals from the optical fiber, for distribution to individual homes.
Various interactive services to be provided by digital transmission systems require a bi-directional link between the central controller and individual subscriber units. One way to provide a return path from the subscriber units back to the central controller is to rely on existing telephone lines. However, it would clearly be advantageous to provide bi-directional communication over the same plant, such as an HFC plant, in which the downstream television signals are provided to the subscriber units. In order to accomplish this, proposals have been made to develop robust upstream communication networks over HFC plants. For example, single carrier frequency and time division multiple access (F/TDMA) have been proposed to provide a low risk, high capacity approach which offers suitable characteristics for upstream modulation over an HFC system.
In order to efficiently implement a practical upstream channel, it would be advantageous to allow the central controller to allocate bandwidth on an upstream channel according to the current subscriber demands. The central controller should have the capability to provide a minimum bandwidth to each subscriber, and to distribute bandwidth among users in an equitable manner. The central controller should also have the capability to provide priority to selected users, such as those who pay an additional fee. The scheme should be applicable to virtually any type of network, including networks which communicate television and/or other data signals, and should operate in a manner which is transparent to the subscriber units.
The present invention provides a communication scheme enjoying the above and other advantages.